Hitherto, a uniformity inspection has been performed which measures the uniformity (evenness) of a product tire and determines whether the tire is good or bad. For example, when a case is exemplified in which the uniformity of an automobile tire is measured, a tire test is substantially performed according to the following procedure by using a tire testing device illustrated in Patent Document 1.
That is, in a case where the tire test is performed by the tire uniformity testing device of Patent Document 1, a tire that is conveyed from the upstream side of an inspection line is first clamped between upper and lower separate rims. Then, the tire is inflated in a short time by using a pipe of a bead seat system. Next, in the tire uniformity testing device, a compressed air passage is switched from the pipe of the bead seat system to a pipe of a test system by using a switch valve. Then, a drum is pressed against the tire maintained at a test pressure, the tire is rotated normally, and a repelling force generated in the tire is measured by using a load measurement unit provided in the drum, thereby measuring the uniformity of the tire. Subsequently, the tire is rotated reversely, and the uniformity of the tire is also measured during the reverse rotation.
Patent Document 2 discloses a tire testing device like Patent Document 1, but discloses a method of causing a contact surface of a load drum to retreat from a tire tread surface during the reverse rotation of the tire and reduces a pressure exerted on the tire during the stop of the tire.
Meanwhile, Patent Document 3 discloses a technology of obtaining a shift gradient of a force variation waveform caused by a warming-up characteristic for one revolution of a tire from a period of one revolution of the tire and a difference between a sampling value of a force variation waveform for one revolution of the tire and a sampling value for the subsequent revolution of the tire based on a result (waveform signal) obtained by a tire uniformity testing device, corrects the force variation waveform so that the gradient becomes 0, and obtains a force variation from the corrected force variation waveform.
Hitherto, a tire test (uniformity inspection) has been performed which measures the uniformity (evenness) of the product tire and determines whether the product tire is good or bad. For example, in a case where the uniformity of an automobile tire is measured, the tire test is substantially performed according to the following procedure by using a tire testing device disclosed in Patent Document 4.
That is, the tire testing device of Patent Document 4 includes an air pressure circuit that supplies compressed air supplied from a factory air supply to a tire placed on a rim while adjusting the pressure of the compressed air. Accordingly, the tire test is performed after the tire is inflated to a test pressure.
In a case where the tire test is performed by the tire testing device, the tire that is conveyed from the upstream side of an inspection line is clamped between upper and lower separate rims. Next, the tire is fixed to the rims while being inflated in a short time by using a pipe of a bead seat system as one of two branched pipes provided in the course of the air pressure circuit. Then, a drum is pressed against the tire that is maintained at the test pressure by the compressed air supplied from a pipe of a test system as the other pipe of two pipes, the tire is rotated normally, and the uniformity of the tire is measured. Subsequently, the tire is rotated reversely, and the uniformity of the tire is also measured during the reverse rotation.
In the above-described tire uniformity measurement method, when the rotation direction of the load drum is reversed from the state where the load drum rotates in a predetermined rotation direction, the rotation of the load drum temporarily stops. If the rotation of the tire stops while a predetermined pressure is applied to the tire, a recessed portion of the tire caused by the pressure of the load drum becomes a remaining recessed portion later (see FIG. 4). This phenomenon is caused by the viscoelastic characteristic of a rubber material of the tire. Then, it takes some time until the remaining recessed portion is restored to the original state, and according to Patent Document 4, it is proved that the measurement precision is largely influenced when the uniformity of the tire is measured in such a state. Thus, there is a need to measure the uniformity of the tire while the uniformity waveform is stabilized after a user waits for the restoration of the tire, and hence a problem arises in that some time is taken.
Therefore, as one of methods of solving the above-described problems, Patent Document 5 discloses a method of causing a contact surface of a load drum to retreat from a tire tread surface before a tire is rotated reversely and reduces a pressure exerted on the tire when the rotation of the tire stops.